Follow-up from "Capture AWS role for creating EKS clusters"

The following discussion from !18307 (merged) should be addressed:

• @tigerwnz started a discussion:

  These three spec files (spec/controllers/admin/clusters_controller_spec.rb, spec/controllers/groups/clusters_controller_spec.rb, spec/controllers/projects/clusters_controller_spec.rb) are very similar, we should open a follow-up issue to move them all into a shared context.